Many pathological conditions in the human body may be caused by enlargement, movement, displacement and/or a variety of other changes of bodily tissue, causing the tissue to press against (or “impinge on”) one or more otherwise normal tissues or organs. For example, a cancerous tumor may press against an adjacent organ and adversely affect the functioning and/or the health of that organ. In other cases, bony growths (or “bone spurs”), arthritic changes in bone and/or soft tissue, redundant soft tissue, or other hypertrophic bone or soft tissue conditions may impinge on nearby nerve and/or vascular tissues and compromise functioning of one or more nerves, reduce blood flow through a blood vessel, or both. Other examples of tissues which may grow or move to press against adjacent tissues include ligaments, tendons, cysts, cartilage, scar tissue, blood vessels, adipose tissue, tumor, hematoma, and inflammatory tissue.
The intervertebral disc 10 is composed of a thick outer ring of cartilage (annulus fibrosus, 12) and an inner gel-like substance (nucleus pulposus 14). A three-dimensional view of an intervertebral disc is provided in FIG. 1. The annulus 10 contains collagen fibers that form concentric lamellae 16 that surround the nucleus and insert into the endplates of the adjacent vertebral bodies. The nucleus pulposus 14 comprises proteoglycans entrapped by a network of collagen and elastin fibers which has the capacity to bind water. When healthy, the intervertebral disc keeps the spine flexible and serves as a shock absorber by allowing the body to accept and dissipate loads across multiple levels in the spine.
With respect to the spine and intervertebral discs, a variety of medical conditions can occur in which it is desirable to ultimately surgically remove at least some of if not all of an intervertebral disc. As such, a variety of different conditions exist where partial or total disc removal is desirable.
One such condition is disc herniation. Over time, the nucleus pulposus becomes less fluid and more viscous as a result of age, normal wear and tear, and damage caused from an injury. The proteoglycan and water from within the nucleus decreases which in turn results in the nucleus drying out and becoming smaller and compressed. Additionally, the annulus tends to thicken, desiccate, and become more rigid, lessening its ability to elastically deform under load and making it susceptible to disc fissures.
A fissure occurs when the fibrous components of the annulus become separated in particular areas, creating a tear within the annulus. The most common type of fissure is a radial fissure in which the tear is perpendicular to the direction of the fibers. A fissure associated with disc herniation generally falls into three types of categories: 1) contained disc herniation (also known as contained disc protrusion); 2) extruded disc herniation; and 3) sequestered disc herniation (also known as a free fragment.) In a contained herniation, a portion of the disc protrudes or bulges from a normal boundary of the disc but does not breach the outer annulus fibrosis. In an extruded herniation, the annulus is disrupted and a segment of the nucleus protrudes/extrudes from the disc. However, in this condition, the nucleus within the disc remains contiguous with the extruded fragment. With a sequestered disc herniation, a nucleus fragment separates from the nucleus and disc.
As the posterior and posterolateral portions of the annulus are most susceptible to herniation, in many instances, the nucleus pulposus progresses into the fissure from the nucleus in a posteriorly or posterolateral direction. Additionally, biochemicals contained within the nucleus pulposus may escape through the annulus causing inflammation and irritating adjacent nerves. Symptoms of a herniated disc generally include sharp back or neck pain which radiates into the extremities, numbness, muscle weakness, and in late stages, paralysis, muscle atrophy and bladder and bowel incontinence.
Conservative therapy is the first line of treating a herniated disc which includes bed rest, medications to reduce inflammation and pain, physical therapy, patient education on proper body mechanics and weight control.
If conservative therapy offers no improvement then surgery is recommended. Open discectomy is the most common surgical treatment for ruptured or herniated discs. The procedure involves an incision in the skin over the spine to remove the herniated disc material so it no longer presses on the nerves and spinal cord. Before the disc material is removed, some of the bone from the affected vertebra may be removed using a laminotomy or laminectomy to allow the surgeon to better see the area. As an alternative to open surgery, minimally invasive techniques have been rapidly replacing open surgery in treating herniated discs. Minimally invasive surgery utilizes small skin incisions, thereby minimizing the damaging effects of large muscle retraction and offering rapid recovery, less post-operative pain and small incisional scars.